Scattering of Be-7 and B-8 and the astrophysical S-17 factor
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Measurements of Be-7 scattering at 87 MeV on a melamine (C3N6H6) target and of B-8 at 95 MeV on C were performed. For Be-7 the angular range was extended over previous measurements and monitoring of the intensity of the radioactive beam was improved. The measurements provide a renormalization of the absolute cross section of existing data on the proton transfer reaction N-14(Be-7,B-8)C-13 and lead to improved optical-model potentials used in the incoming and outgoing channels for the distorted-wave Born approximation analysis. The results yield an updated determination of the asymptotic normalization coefficient for the virtual decay B-8 -> Be-7+p. The new value, C-tot(2)(B-8)=0.466 +/- 0.049 fm(-1), is slightly larger than, but consistent with, the previous result. This implies an astrophysical factor, S-17(0)=18.0 +/- 1.9 eV b, for the solar neutrino-generating reaction Be-7(p, gamma)B-8.